Many conventional power expanded mandrels utilize a draw rod which, in response to longitudinal movement thereof, causes radial movement of the mandrel segments through interengaging wedges, links or the like. Longitudinal movement of the draw rod is accomplished by means of hydraulic cylinders exerting a direct pull on the draw rod.
With this arrangement it is generally considered impractical to mount the hydraulic cylinders for the draw rods on the free end of the mandrel, since they are prone to damage when positioned in this manner. Therefore, the hydraulic cylinders for the draw rods are generally located adjacent the driven end of the mandrel. Thus, however, requires a hollow shaft thru the drive mechanism and precludes the use of drives which do not have hollow shafts.
It will be seen, therefore, that in prior art, power operated mandrels if a drive without a hollow shaft is desired, the draw rod hydraulic cylinder must be positioned on the free end of the mandrel where it is subject to damage. On the other hand, if the draw rod cylinder is mounted on the motor end of the mandrel shaft, the use of a drive without a hollow shaft is precluded. Additionally, in either case, separate drive means must be provided for the mandrel and the draw rod.